There is known conductive paste having metal particles dispersed in a vehicle of an organic binder and a solvent. Conductive paste is used for formation of a conductor pattern for a printed circuit board, formation of an electrode for an electronic part, and the like. Such conductive paste may be roughly classified into a resin curing type and a firing type. Conductive paste of the resin curing type is conductive paste having conductivity secured by making metal particles contact with each other due to curing of a resin. Conductive paste of the firing type is conductive paste having conductivity secured by sintering metal particles with each other due to firing.
As the metal particles contained in the conductive paste, copper powder and silver powder, for example, are used. Copper powder is advantageous in excellent in conductivity and more inexpensive than silver powder. However, copper powder is prone to be oxidized in an air atmosphere, so that it is disadvantageous in that, after forming a conductor pattern on a substrate, for example, a surface of the conductor pattern has to be coated with a protective material. In contrast, silver powder is advantageous in that it is stable in an air and that a conductor pattern may be formed by firing in an air atmosphere while it is disadvantageous in that electromigration is prone to occur.
As a technique to prevent electromigration, Patent Document 1 discloses conductive coating that has silver powder, as a main conductive material, characterized by containing from 1 to 100 parts by mass of powder of manganese and/or manganese alloy based on 100 parts by mass of silver powder. Patent Document 2 discloses conductive paste characterized by containing a binder resin, Ag powder, and at least one metal or metal compound selected from the group of Ti, Ni, Sn, and Sb.
However, the conductive paste disclosed in Patent Documents 1 and 2 is insufficient in the adhesion to a substrate and the soldering heat resistance, and there used to be a practical problem when it is used for formation of a conductor pattern on a substrate.
Then, as a technique to improve the soldering heat resistance of conductive paste, Patent Document 3 discloses conductive paste characterized by that silver powder is coated with a material containing a first metal component to inhibit sintering of silver and a second metal component to promote sintering of silver.
However, while the conductive paste disclosed in Patent Document 3 has improved soldering heat resistance to a certain extent, sintering of silver is inhibited, so that there used to be a problem of decreasing the conductivity of a conductor pattern obtained by firing the conductive paste. In addition, since a step of coating a surface of silver powder with a metal material is required, there used to be a problem of complex production steps.